Process for the recovery of copper from its ores and minerals



MCGAULEY ETAL PROCESS FOR THE RECOVERY OF COPPER C a 5 /Pf-Rz cav/[N7 FROM ITS ORES AND MINERALS 65504 Fea ($04)3 l i700/- w. W G

rem 0 Vea from s ys fem Wafer (as necessary] app er i M@ a/ Reduc/)3y Gas Copper- Bear/)gy Press cake I N V E N To R 5 P4 TP/C/f d. /Wc Maz fr, FDM/41?@ 6. POEf/P, gm 37% I ATTORNEY llllllll Il Waff/- (05 necessary) Sept. 25, 1951 Filed June 4, 1949 l Pes/'daa/ Copper fr; Jo/n. (ITam/anke@ 401302 of Sept. 25, 1951 p J, MGGAULEY ETAL 2,568,963

PROCESS FOR THE RECOVERY OF COPPER FROM ITS CRES AND MINERALS Filed June 4, 1949 2 Sheets-Sheet 2 OFF CONCENTPfQfE C 504 fama/Pp 5. P055@ 71s ATTORNEY Patented Sept. 25, 1951 PROCESS FOR THE RECOVERY OF COPPER FROM ITS ORES AND MINERALS Patrick J. McGauley, Glen Cove, and Edward S.

Roberts, New York, N. Y., assignors to Chemiycal Construction Corporation, New York, N. Y., a corporation of Delaware Application June 4, 1949, Serial No.-97,224

(Cl. l-115) 4 Claims.

.Thisinvention :is concerned withproduction Iof powdered metallic copper. It 4deals witliproc- 1-esses -whereby copper-bearing mixtures, .particui-larly=mixtures of copper-bearingand iron-bearfingminerals, are treated to convert thecopper content to coppersulfate; and `subsequently cop- :yper is precipitated froma solution of the sulfate.

.Morefparticularly vthe-present invention. is con- .cerned with-.the treatment of such copper-bear- -fng mixtures Ato obtain an enriched. concentrate of copper sulde by replacing other .metals .with copper. Still more '-speciically, in precipitating the powdered coppenmetal, onlythat portion of `the copperavailable, =as copper sulfate, is .precipi- .tatedWhichf-can-be=lbrought -down Vin suicient pur-ity. The yresidual/available copperiin solution is used `to eliminatecther metalssuch .as the @iron-noted above, from thesystem in the replacement reaction.

Many of I `the ...dissolving operations previously :..proposed werenot .as universally..adaptableas might be desired. Some `were vessentially. limited Vto-the treatment of oxidized v.copper .minerals GthersV were really suitable only7 for .sulfide ores. -Many-were inefficient and/ or required excessive equipment -Some'lost their eiiiciency when salts off-iron, orother 'metals higher than copperin -theelectromotive series,-vvere p-resent-in the` ore. None were suitable Y.for treatment of materials yhaving present notonlyfoxidizedcopper and-copf-.per :sulfide-:minerals -but also. iron suldes.

In`-addition tothe problem of separating the -copperfrom the ganguematerial, by .placing it .in solution, there is also the problem of obtain- `ing the'copper chemically from solution.` Again, proposals to overcome a-number of obstacles .have-beenmade. `However, in noneof the previousproposalsvhave all of theseobstacles .been #successfullyovercome. 'Among others, .for lex- -amplefthe processes involve steps which could 4.not yreadilybe yadapted to continuous production; or were necessarily restricted tothe recovery of limited= amounts of ore. A- Others `produced the `metal in forms unsuitable for industrial use. Some.processesamounted-.to nomore than purication-of copper-.previously obtained by some othenmethod -This problem of vproduct purityV is particularly .-.troublesome `Copper 'metaL to be industrially saleable must meet so-called electrolytic standards. Inother-words, the copper content of the metalf..p1us vany lminor silver content, must be 99.9% or-better. `v`In vthe'past, the chemical proc- -essesI which' were available either couldr not pro- :.duce-f-coppercof this-f purity or if capable of approximating this .purity,;did,not voperate with. a commercially useful eicency .in recovering Athe copper.

Nevertheless, .there .is a .constantly increasin demand for a .procedureof this type which is not subject to the limitations and difficulties of these earlier attemptsat chemical leaching and chemical precipitation. It is, therefore, a Yprincipal object of the .present invention to provide .a method capable of economically concentrating the copper svaluesl nin the source materials, converting .the concentrate to asolution .of ,copper salts and chemically .precipitating` copper fromk :a solution of. those salts.

Quite surprisingly,,particularly in view ofl-the long period of time over which a process. has been found desirable without its beingdevelopedthe 4`problem hasbeen solvedby a continuous process which fulfills fthe., desired objects. Asis noted above, apr-incipalieature of thisnovel processis .its utilization of areplacement reaction, whereby -the-copper content-..of..the feedY` is augmented .by .copper -sulfide precipitated in the elim-inationof r.other .metals.fromthesystem ,Having obtained,..by.means ofthe replacement .-reactioman.enriched copper-.bearing slurry, .in .which the Ycopper .content .is` considerably higher than ...in .the ..materials bein-g treated, the .re- .mainder of the process. isfstraightforward. The `enriched slurry .is subjected to oxidationzin. the presencev of excess sulfuric acid, the .copperibeing. converted to: copperrsulfate in solution,.eit-her .directly oraftera purification Yin which thesalt is .separated out by .crystallization and redis- `solved, andistreated -Withcarbon monoxide to precipitatepart of thecopper content thereof rwith carbonmonoxide.

-When thusbroadly. stated, the process .appears simple. In its.entirety,.however,.the appearance f`is more deceptivethan real. .In its entirety, Vthe `-processhis ,essentially the .combination of steps, several of which are necessarily novel. .In.,each .of thestepsa considerabledegree of .care must :be exercised.

v.The overall 4process .embodying the vessential featuresL ofthe .present invention may .probably Abe .more readilyunderstoodby being describedin conjunction with ythe accompanying vdrawing. `The `latter .constitutes .simplified ow ,sheets showing the basic operations. of thecombina- .-tion. of steps which, when taken together,-com

prise-the lprocess of` the `present invention.

VrFigure 1 is a flow sheetshowing `one modification `of. .they general. procedure; .and

Egure. is anadditionaliiow sheetshowinga 'amounts of soluble iron sulfate.

useful modication in which feed is pretreated before being passed to the process such as that of Figure 1.

As will be seen by reference to Figure 1, material treated in the present process is designated as concentrate orfore concentrate.

While itis perfectly feasible to adjust the proces's of the present invention to treat ore as mined,

placement. This step constitutes one of the more novel features of the process of the present invention. It is highly flexible and may be adjusted to cover many different operation conditions, and to cope with the requirements presented by many different ores. Its flexibility will be more fully discussed below.

As shown in Figure 1, it is used in perhaps its most simple combination, with the other steps of the present invention.

In actually carrying out the operation, several different materials are fed to a replacement tank. One of these is the feed or ore concentrate. Another is an aqueous acid solution containing free copper ions. As shown in Figure 1,v additional acid is also provided by a sulfuric acid ferrc sulfate liquor. Once operation is stabilized, these solutions will be furnished by recirculation. In Figure 1, it is assumed that operations are in equilibrium and are in normal fiow during continuous operation.

It is to be noted that copper ions are fed to the tank in one solution and a different solution, comprising sulfuric acid and ferric sulfate, is also fed to the tank.v The iron, as so fed, does not enter into the actual reaction, but, as Will be noted below, passes through this operation in being removed from the system. Actually, these two solutions need not be separately fed. 'Ihey may be one single solution. Copper ions to start operations may be obtained by dissolving copper sulfate or by leaching an ore containing oxidized copper minerals with sulfuric acid. Sulfuric acid, in starting operations, may be furnishedf directly as aqueous sulfuric acid solution.

In Iany case, Whether by special solution or by recirculation, the concentrate is treated in the replacement tank with copper ions and in acid solution. The net result is the replacement ofy solved copper salts. In this way, replaced iron4 sulfide from the feed solids is converted to soluble ferrous sulfate.

While it is essential to strip all copper from the solution of copper salts entering the replacement tank, this result does not depend on any particular copper-iron ratio in the liquor at any one time. It is essential only that sufficient iron be added in the feed solids to be at least equivalent to the copper in solution. Experience has shown that the aqueous sulfuric acid ferric Asulfate treating liquor, as introduced, should contain about 5-15% sulfuric acid and may contain varied Y Since all the ferric sulfate must be reduced to ferrous sulfate before any effective replacement can ocul,

it is desirable to keep the ferrie sulfate low, although it is inevitable that some be present, as will be seen from further considerations below. In ordinary operations, the ferrie sulfate may run about 2-15%. Such liquors are readily obtained by recirculation from subsequent steps in the fiow sheet.

At the end of the replacement reaction, materials will be present in the form of a slurry. This slurry is drawn from the tank and filtered, as shown in Figure 1. From the filter is obtained a copper sulfide presscake, in which the copper sulfide content is much higher and the iron sulfide content is much lower than was found in the voriginal feed concentrate. This presscake is carried through the remainder of the process of the present invention.

The filtrate obtained in this operation is sent out of the circuit of the present process. So far as the latter is concerned, this lconstitutes the principal point of discard. The liquor sent from the circuit is substantially barren of utilizable copper content. It will contain, however, besides the ferrous and ferrie sulfates, an assortment of miscellaneous soluble dissolved salts. Among these may be found those of zine, nickel, cobalt, and the like. The filtrate, therefore, may'not be Valueless. It is not an actual discard in such cases but is sent to some further processing which, since it forms no part of the present flow sheet, is not shown.

In the more direct line of the present process, it is the copper sulfide presscake which is sent to the oxidation tank. In this step, the presscake is treated with sulfuric acid and ferrie sulfatesulfuric acid solution. Ferric sulfate, for the operation, is obtained by recirculation. In starting up, it can be dissolved especially and added for the purpose. Y

Oxidation is conducted under heat and pressure. In most cases the temperature conditions will range from about C. up to about 325 C. Preferably, the operating temperature is maintained as low as is possible for the characteristics of the ore being treated. Operating pressure will depend upon whether the oxidizing gas is oxygen, air or oxygen-enriched air. When using oxygen, the pressure at the higher end of the temperature range may go up to 350-500 pounds per square inch gauge. Using air, at these temperatures. pressure may range up to about 50o-750 pounds per square inch gauge.

Once the oxidation reaction begins there is no problem in obtaining these conditions. On the contrary, the reaction is highly exothermic and it Will be necessary to bleed steam from the tank in order to keep below the maximum desirable temperature and pressure conditions. Actually, there is no particular harm in going above the stated temperature and pressure conditions. Since it is not necessary to do so, such practice is uneconomical and may not be possible in equipment which is otherwise usable. The oxidized product, so far as the present invention is concerned, will constitute principally a solution of copper and iron sulfates. Usually in addition thereto there will be a considerable amount of gangue. To eliminate the latter, the oxidized slurry is ordinarily filtered. The filtrate or sulfate solution is passed to further processing to recover copper by any suitable method. One such is shown in Figure 1. The presscake, or gangue, is removed from the system.

This filtered sulfate solution is at a relatively high, temperature, usually about 100-110 C., and

mesma therefrom mustebe cooled. It'uwill-:be supersatufrated :with copper sulfate :when: it` isV cooled; The resultant .slurry is,. therefore; usually.l sent?4 to 'a copperf sulfate separator in.x.which the; copper sulfate. crystals are collectediandf: the i mother liquor, comprising aqueous sulfuric acid-torrie sulfate liquor, is recycledi Certain types of 'apparatusV are available. inv which both the.; cooling and. the crystal-'collecting operations may-be simultaneously conducted.. When using such` equipment, the. tWo steps as shoWnin-Figure 1 maybe combined into a -single operation;

Before continuing with; the "treatment:ofz-V the copper sulfate, it `perhaps should .be Anoted :how

the, residual mother liquor ,isrecirculated Pure copper sulfate can: be crystallized from solutions. containing both coppenandiron: sulfatos only asylong' as the copper-iron ratio-isf 'greater ythan onen'.i It; a principalY purposeofffthe'replacementreaction to iavorablyfalter this ratio. However, if there is any ironiimthe. system-,'-therefwill always be considerable; amounts Vof this' liquor after -fcrystallizationx f This liquor, after 'f crystal separation, Will` constitute sulfuricacid-ferrie sulfate solution of approximatelyrthe, correct acid "content to be used fin. thefcopper replacement reaction.' It is; therefore," recycled principally for this purpose.y Howevenone other feature should be noted.4 While sulfuricr--acidsisfproduced `from iron suldes in the oxidationfstep; Water islost, due tothebleeding. ofsteam. It is necessary to replace theylatter'.l Therefore, any excess of mother-liquor, over that-whichfis required forthe replacementv operation, is recycled to the oxidation tank.- Anyfcirculating load ofexcess Yferrie vsulfate VWhich-this, causes hasno appreciable effect` on' the overall capacity.'

Continuing with the preferred copper-recovery-A treatment, crystalsfobtainedA fromcthe separator are dissolved. In this connection; several other points vmight -benoted; The solution leaving the oxidizing tank isl at a relatively Vhigh temperature and contains a highI copper sulfate content, soA that it becomes readily supersaturated. Accordingly, it may be,` and usuallyrmust ybe,-diluted 'at various points to prevent crystallization in other apparatus before the -temperature isfdownto its; boiling point at atmospheric pressurew This:` water Will usuallybeaddedinblowing the-slurry from the `'oxidation tank to 'insure against 'solidiiication in the rreduction valve: It vmay be^added; directly-to the tank. ThereA is adequate 'solubility differential between the-boiling -pointf at atmospheric pressure and temperatures readily obtained inthe cooler to insure-adequate crystal separation.

Crystals ofcopper sulfate f obtained fromA l-.th'eV` separator are dissolved andthe solutionf istreatedftofrecover copper metal. @nesuitable-processY therefor forms the subject matterofthe copending applications for United States Letters PatentY Ser. No. 86,156, liled lAugust. 8'; 1949-, by E. S;Y Roberts, one ofthe present inventors.

According to Ythe teachings'therein; thesolu-4 tion is' sent to'a reduction tank. In this tank,'the solution is treated with'coppermetalandv satu-A ratediwith a reducing gas. Theresultis; the reduction of a substantial portion, if notfall, of Vthe'- copper ions fromthe cuprictothe -cuprous condition.

Copper metal is ordinarily'usedrincarrying outthe reaction. It maybe 10W-grade copper,- i`. e., cement copper or the like or it may be scrap copper' previously utilized for some-otherpurpose However, since thereis no nalloss-offthegmetal-z peri-carbonmonoxidefis blownginto the solution".

lllhis Ashould be carried out-until the solution be-c comesfsaturated .With,;thegas.g 'IO insure. its4 abs sorption, the temperature should be as` low f as is.Y practicable'.Y As will `beseen from-the natureof the -ow sheet, therefis no particular problem .in obtaining such: temperatures.

Solution, saturated;With reducing gas, is theny passed; to continuous autoclave',Y ingA which it is treated to prec-ipitatefa lpart-ofl the coppermetal c content. Preferabl-ygan*atmosphere; of the -reducing gas of about 10D-150 pounds perfsquarevr inch gauge, in excess-f of the vapor pressure is maintained on the autoclave :and reaction is carried out at about l200-2'7-5-C; SomewhatA higher' temperatures andfDressu-res may be ,used if Iit is necessary or desirable to doso.:

At this point,- it may:'begwellgtio consider the possibility-of variationsrin the; normal floWz.. For: ther moment, consider thematerial leaving the f: oxidation tank. Int-treating someA sourcemate-- ria-ls', thel gangue,contentfofthisexit material will be small; If sof-the nlteringstep may be by-` passed; because the1fllter, ,WhichsfolloWs-thenreduction step; will remove-these small amounts of? gangue. VIn isuchgwcase; the; amount of, Copper. metall, which; leaves thefreductiQn--step should `beil maintained lovv; and-.ftheregbeingno particular copper content therein-, it can be discarded, rather than recycled to 'the replacement operai tion. Y The-solution leaving` the oxidation tank, in

thatV case, will` be passed 'directly -to the :coolen Further, in treating some, materials, Withl suicient' care,- a` comparatively pure copper sulfatesolution can be Vtaken from the oxidation tank.

When that occurs either of two alternatives may be open. Solutionfrom the oxidation tankmay# be placed directly in` the --reduction step, the necessary cooling being Iprovided-either` by dilution:

in the oxidation-tankin--the reducing valve, or by ,i adding suicient amount of Water to the-reduction tank; The-second alternative is to pass theY solution-to.4 the coo1er`andfrom the cooler,-the

resultant slurryis passedftoa dissolvingftank'in which suicient Wateris adr1ed-toinsurecompleteX solution ofcopper; salts: Agairninv this situation,

thesolution/from the dissolver may be rdecanted,A leaving anyv small amounts of gangue inthe ta from which it can be discarded.

Returning to theconsideration of themainm` 1 now; -lteredsaturated reduced'copper solution is passed'to an autoclave; As was noted above, sevcarriedn out.' pressure ranges have been-'stated above.

treating time;` Thesethree factorsf'areV sobalanced as -to precipitate onlyya part of`theavailable-copper;l this? beinel :critical forrseyeral rea- As was noted above, product copper must have a copper contentof 99.9% or greater. It is a particular advantage of the present invention that it is perfectly feasible to produce continuously the copper powder which will analyze 99.9499.99% pure copper.

To insure this result, it is necessary to precipitate only part of the available copper in the autoclave. The requisite grade is obtained only when the copper is precipitated under certain conditions. Precipitation should be stopped when the precipitate falls below this grade. Experience has shown, that optimum operation, to insure the desirable result, usually constitutes precipitating about 60-70% of the theoretically available copper in the solution coming to the autoclave. Of course, a smaller amount may be precipitated but it is not eicient to do so. In some cases, it is possible to go well above the 70% limit.

The remaining solution, containing unprecipitated copper equivalents, is recycled. Ordinarily, it is recycled to the replacement operation. This is, as noted above, a novel operation in this invention. The extent of the replacement is governed, to some extent, by the iron sulfide content in the feed.

Most ore concentrates which require treatment by the present process, will contain suiiicient iron to more than utilize any copper recycled to the replacement. Where the iron content is low, the feed rate is simply stepped up. If the iron content is so low that this will overload the apparatus, the ore does not require treatment by the' present invention. Such ores do exist, but are becoming more and more scarce.

Some ores will contain iron in excess of those amounts which can be handled without using the replacement operation of the present invention, but not sufficiently at desirable feed rates to utilize all the copper which it is desirable not to l precipitate in the autoclave. For that purpose,

an optional fiow line is shown in the drawing. The excess copper solution, in that case, is returned directly to the oxidation tank.

It will be noted from the foregoing that the replacement operation is highly flexible in its capabilities. In the overall process of Figure 1, it can handle any type of ore concentrate containing mixed sulfides of iron and copper, and also copper oxide minerals, if they are present. The ironzcopper ratios in the feed, which can be treated according to the process of Figure 1, range from those which are just too high to be treated without operating the replacement reaction, up to those in which the iron:copper ratio is somewhat higher than that required to precipitate all the copper in the solution which it is desirable to recycle as autoclave discharge. This covers a rather Wide range.

It should be noted that the final production of pure copper metal powder not only involves partial precipitation in any one cycle, but preferably utilizes a certain amount of copper for a reduction operation. These features, as noted, were discussed in the copending application for United States Letters Patent, Serial No. 86,156, of E. S. Roberts. While any other process which provides a solution containing copper ions for recycling may be substituted, if so desired, this treatment is highly desirable in an optimum operation. While only a portion of the available copper in the autoclave is precipitated, the overall process is really substantially one hundred percent efficient. The recycled copper ions is in amount a substantially continuously circulating load. Precipitated copper, over and above that added in the reduction step as copper metal, will constitute substantially one hundred percent recovery of the copper content of the feed at the rate at which it is being treated during continuous operation.

It is readily possible, by a slight modification of the flow sheet, Figure 1, to provide for the handling of ores having a much higher iron content. Such a procedure is briefly shown in Figure 2. The process shown in Figure 2 differs essentially from that of Figure 1 only in providing for a preliminary oxidation.

As shown in Figure 2, feed concentrate is not passed directly to the replacement, as in Figure 1. Rather, a part of the feed is passed to a preliminary oxidation tank. In this tank, the same operation is carried out as was done in the oxidation tank previously discussed in connection with the process of Figure 1. The same general operation conditions should apply.

' Oxidized slurry obtained from this tank is passed to a suitable preliminary filter, preferably of av continuous type, presscake from this filter is discarded from the operation of the present process. Filtrate from this preliminary filter, which will contain one mol of dissolved copper for each mol of available copper in the feed to the preliminary oxidation, is used to treat additional amounts of feed concentrate in the replacement tank. Operation of the replacement is otherwise the same as the flow of Figure l. As a net result, a slurry is obtained which will contain the copper sulfide of the concentrate fed to the replacement, plus copper sulfide in amounts equivalent to the copper in solution in the preliminary filtrate and in the recycled autoclave liquor.

After filtration, the presscake has an iron content which is less than the total in the feed, by the soluble ferrous sulfate equivalent of the available copper in solution, and that converted to ferric sulfate in the preliminary oxidation. Thus, the copper:iron ratio in the feed to the oxidation tank is quite high, as compared to the ratio in the feed concentrate. The filtrate which contains the ferrous sulfate and other` soluble miscellaneous ions, is sent, as in Figure 1, to some further treatment. The oxidation tank, to which the copper sulfide presscake is taken, corresponds exactly to the oxidation tank in the process of Figure 1. It again is operated under the same general requirements and a sulfates solution is produced in the same way.

To indicate similarities in the fiow, from this point on, in Figure 2, the start of the treatment of this oxidized slurry is shown. It is filtered, the gangue being removed from the system, the filtrate cooled, and the cooled slurry sent to the copper sulfate separator. From the latter, the mother liquor is recycled. Since, in this flow sheet two oxidation reactions are being carried out recycling the mother liquor is done to both tanks as needed. The requirements of the principal oxidation tank is first supplied, and any excess is used in the preliminary oxidation tank. The copper sulfate product which is obtained from the separator is then dissolved and treatment continued, as in the process of Figure 1.

It is lbelieved that the operation of the process of the present invention is clearly apparent from the foregoing discussion. Briefly summarized, it constitutes a combination of steps. A mixed copper ore is treated with copper ions in solution and with a sulfuric acid-ferric sulfate solution,

which by replacement produces an enriched copper sulfide slurry and reduces the iron sulde content. The enriched copper sulfide presscake, containing some iron suldes, is subjected to oxidation in the presence of sulfuric acid. If necessary, these steps may be repeated as shown in Figure 2. In either case, the resultantsolution is treated to obtain copper sulfate. IA solution of the latter, preferably after purification by crystallization and redissolving, and preferably in the form of cuprous ions by reduction, is the treated to precipitate about 60-70% of its coppell content, as powder meeting the electrolyti'c standards. The residual dissolved copper, together with the copper sulfate mother liquor, is also recycled to the replacement tank, wherein it is used to treat additional fresh feed.

We claim:

1. An improved process for treating a copperbearing solids mixture, at least a part ofv which comprises suldes of copper and of ironand in which the copper-iron ratio is too low for effective recovery of copper by direct acid leaching, to dissolve and recover the copper contentthereof while eliminating iron, which process comprises: admixing a portion of said solids mixture with a volume of aqueous sulfuric acid treating liquor containing copper ions, said portion of solids having an iron content chemically equivalent to at least a major portion of the dissolved copper in said liquor; continuing the treatment'j of said solids with said volume of liquor until precipitation of copper'froxn solution as copper sulfide with the concomitant solution of a chemical equivalent of iron as ferrous sulfate substantially the copper and iron content thereof is converted 4 to a solution of dissolved sulfates; removing cop- .10 Number Name Date 924,076 Jumau June 8, 1909 1,588,806 Pike et al. June 15, 1926 FOREIGN PATENTS 5 Number Country Date 15,849 Great Britain 1911 l0 per from said solution in amount substantially equivalent to the copper dissolved from said portion of said solids and returning the residual copper bearing liquor as treating liquor for an additional portion of solids mixture.

2. A process according to claim 1, in which one portion of said solids mixture is subjected to a preliminary oxidation in the presence of a solution containing ferric sulfate and an excess of sulfuric acid, with a member of the group consisting of oxygen, air, and oxygen-enriched air; the resultant treated slurry is filtered; the presscake is removed from the circuit; and the filtrate is used as a part of said treating liquor.

3. A process according to claim 1, in which said gaseous oxidation is carried out with a meinber of the group consisting of oxygen, air, and oxygen-enriched air, said oxidation being exothermic; su'icient steam is bled from the reacting mixture to prevent the temperature exceeding about 325 C. and suiicient water is introduced into the reacting mixture to` maintain all the soluble sulfates in solution at the reaction temperature.

4. A process according to claim 3, containing the additional steps of cooling the resultant sulfates solution, whereby a part of the copper sulfate is crystallized, collecting the crystallized copper sulfate; recycling a portion of the residual liquor as leaching solution and the remainder as part of said treating liquor.

PATRICK J. MCGAULEY. EDWARD S. ROBERTS.

REFERENCES ciTED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

1. AN IMPROVED PROCESS FOR TREATING A COPPERBEARING SOLIDS MIXTURE, AT LEAST A PART OF WHICH COMPRISES SULFIEDES OF COPPER AND OF IRON FOR EFFECWHICH THE COPPER-IRON RATIO IS TOO LOW FOR EFFECTIVE RECOVERY OF COPPER BY DIRECT ACID LEACHING, TO DISSOLVE AND RECOVER THE COPPER CONTENT THEREOF WHILE ELIMINATING IRON, WHICH PROCES COMPRISES: ADMIXING A PORTION OF SAID SOLIDS MIXTURE WITH A VOLUME OF AQUEOUS SULFURIC ACID TREATING LIQUOR CONTAINING COPPER IONS, SAID PORTION OF SOLIDS HAVING AN IRON CONTENT CHEMICALLY EQUIVALENT TO AT LEAST A MAJOR PORTION OF THE DISSOLVED COPPER IN SAID LIQUOR; CONTINUING THE TREATMENT OF SAID SOLIDS WITH SAID VOLUME OF LIQUID UNTIL PRECIPITATION OF COPPER FROM SOLUTION AS COPPER SULFIDE WITH THE CONCOMITANT SOLUTION OF A CHEMICAL EQUIVALENT OF IRON AS FERROUS SULFATE SUBSTANTIALLY CEASES, SAID VOLUME OF LIQUOR BEING AT LEAST SUFFICIENT FOR ITS COPPER CONTENT, TO PRODUCE IN THE SOLID RESIDUE A COPPER-IRON RATIO APPRECIABLY GREATER THAN UNITY; FILTERING THE TREATED MIXTURE; REMOVING THE FERROUS SULFATE-CONTAINING FILTRATE FROM THE CIRCUIT; TREATING THE RESULTANT COPPERSULFIDE-ENRICHED PRESSCAKE BY GASEOUS OXIDATION IN THE PRESENCE OF AQUEOUS SULFURIC, WHEREBY THE COPPER AND IRON CONTENT THEREOF IS CONVERTED TO A SOLUTION OF DISSOLVED SULFATES; REMOVING COPPER FROM SAID SOLUTION IN AMOUNT SUBSTANTIALLY EQUIVALENT TO THE COPPER AND RETURNING THE RESIDUAL TION OF SAID SOLIDS AND RETURNING THE RESIDUAL COPPER BEARING LIQUOR AS TREATING LIQUOR FOR AN ADDITION PORTION OF SOLIDS MIXTRE. 